The present invention relates to a centrifugal fluid pump apparatus, and in particular to a centrifugal fluid pump for pumping a medical fluid, such as blood.
In recent medical treatment, centrifugal blood pumps are increasingly used in artificial heart/lung units for extracorporeal blood circulation. Centrifugal pumps of the magnetic coupling type wherein a driving torque from an external motor is transmitted to an impeller through magnetic coupling are commonly used because the physical communication between the blood chamber of the pump and the exterior can be completely excluded and invasion of bacteria is prevented. The centrifugal blood pump includes a housing having a blood inlet port and a blood outlet port and an impeller rotatably accommodated in the housing to feed blood by a centrifugal force generated during its rotation. The impeller, having a permanent magnet disposed therein, is rotated by a rotor having magnets for attracting the magnet of the impeller thereto and by a rotational torque generation mechanism having a motor for rotating the rotor. The impeller rotates without contacting the housing, with the impeller being attracted to the side opposite to the rotor-disposed side by a magnetic force. This state is termed a magnetic levitation state.
When a failure or malfunction occurs in the control system of the magnetic bearing of the conventional centrifugal pump, however, it is impossible to maintain the function of the centrifugal pump by rotating the impeller.
The centrifugal pump of a magnetic levitation type has three sensors for detecting the position of the impeller and three impeller attraction electromagnets. In the control of the magnetic bearing to be executed in the centrifugal pump, the position of the impeller is controlled by controlling electric current to be applied to the electromagnets, based on information of the impeller provided by the sensors for detecting the position of the impeller. Thus, if devices forming a portion of the control system should fail, for example, if cables for the position sensors and for the electromagnets break, the control system will encounter a failure and proper control cannot be accomplished. Thus, it is difficult to rotate the impeller by means of the magnetic bearing in a magnetic levitation state under these circumstances.
It is an object of the present invention to provide a centrifugal fluid pump apparatus allowing rotation of an impeller without substantial contact between the impeller and an inner surface of a housing by utilizing pressure generated by a hydrodynamic bearing when the control system of the magnetic bearing encounters a failure or malfunction, to thereby maintain feeding of a liquid.